Since the all uppercase topic seems to still be hotly debated, I thought I’d write a quick update. It appears there was a research study done in 2007 that I missed when I first wrote the post. The research confirms, as I said 8 years ago, that:

All uppercase letters are not inherently harder to read.

All uppercase letters don’t slow down reading speed.

In fact, in this study, done with both normal vision and low vision readers, people with low vision performed BETTER with all uppercase letters, presumably because they were larger.

This better performance effect with all uppercase disappeared when they increased the size of the font so that it was large even in upper and lower case.

All uppercase letters did not slow down the normal vision people.

It’s a small sample size, but it was statistically significant, and so far as I know there is still no research showing the opposite, so, I’m sticking to the idea for now, that all uppercase letters are not inherently harder to read.